Axial flux permanent magnet motor for ball screw cam elevator mechanism for reduced-head hard disk drive

ABSTRACT

An approach to a reduced-head hard disk drive (HDD) involves an actuator elevator subsystem that includes a ball screw cam assembly with an axial flux permanent magnet (AFPM) motor affixed to a cam screw to drive rotation of the screw, which drives translation of an actuator arm assembly so that a corresponding pair of read-write heads can access different magnetic-recording disks of a multiple-disk stack.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims the benefit ofpriority to U.S. patent application Ser. No. 16/513,585, filed Jul. 16,2019, which claims the benefit of priority to U.S. Provisional PatentApplication No. 62/700,777, filed Jul. 19, 2018; to U.S. ProvisionalPatent Application No. 62/700,780, filed Jul. 19, 2018; to U.S.Provisional Patent Application No. 62/702,163, filed Jul. 23, 2018; toU.S. Provisional Patent Application No. 62/702,154, filed Jul. 23, 2018;and to U.S. Provisional Patent Application Ser. No. 62/747,623, filedOct. 18, 2018; the entire content of all of which is incorporated byreference for all purposes as if fully set forth herein.

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/916,730, filed Oct. 17, 2019; the entirecontent of which is incorporated by reference for all purposes as iffully set forth herein.

FIELD OF EMBODIMENTS

Embodiments of the invention may relate generally to a reduced-head harddisk drive having an actuator elevator mechanism and particularly toapproaches to driving a low-profile ball screw cam actuator elevatormechanism.

BACKGROUND

There is an increasing need for archival storage. Tape is a traditionalsolution for data back-up, but is very slow to access data. Currentarchives are increasingly “active” archives, meaning some level ofcontinuing random read data access is required. Traditional hard diskdrives (HDDs) can be used but cost may be considered undesirably high.Other approaches considered may include HDDs with extra large diameterdisks and HDDs having an extra tall form factor, with both requiringlarge capital investment due to unique components and assemblyprocesses, low value proposition in the context of cost savings, andbarriers to adoption in the marketplace due to uniquely large formfactors, for example.

Any approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a plan view illustrating a hard disk drive, according to anembodiment;

FIG. 2A is a perspective view illustrating an actuator subsystem in areduced-head hard disk drive, according to an embodiment;

FIG. 2B is an isolated perspective view illustrating the actuatorsubsystem of FIG. 2A, according to an embodiment;

FIG. 2C is an isolated plan view illustrating the actuator subsystem ofFIG. 2A, according to an embodiment;

FIG. 3 is a cross-sectional side view illustrating an actuator elevatorassembly, according to an embodiment;

FIG. 4A is an exploded view illustrating a low-profile ball screw camassembly, according to an embodiment;

FIG. 4B is a partial cross-sectional view illustrating a portion of thecam assembly of FIG. 4A, according to an embodiment;

FIG. 4C is a partial cross-sectional view illustrating a portion of analternative cam assembly, according to an embodiment;

FIG. 5A is a perspective view illustrating an actuator-elevatorassembly, according to an embodiment;

FIG. 5B is a plan view illustrating the actuator-elevator assembly ofFIG. 5A, according to an embodiment;

FIG. 5C is a perspective view illustrating the actuator-elevatorassembly of FIG. 5A in a reduced-head data storage device, according toan embodiment;

FIG. 6A is an isolated perspective view illustrating an actuatorposition sensor and flexible cable assembly, according to an embodiment;

FIG. 6B is a perspective view illustrating the assembly of FIG. 6Aassembled with the actuator elevator assembly of FIG. 3, according to anembodiment;

FIG. 7 is a perspective view illustrating an actuator subsystem in areduced-head hard disk drive, according to an embodiment;

FIG. 8 is a cross-sectional side view illustrating an actuator elevatorassembly including an “external” axial flux permanent magnet motor,according to an embodiment;

FIG. 9 is a cross-sectional side view illustrating a portion of anactuator elevator assembly including an “internal” axial flux permanentmagnet motor, according to an embodiment;

FIG. 10A is an exploded view of an axial flux permanent magnet motor,according to an embodiment;

FIG. 10B is an exploded view of the axial flux permanent magnet motor ofFIG. 9A, according to an embodiment; and

FIG. 11 is a flow diagram illustrating a method for verticallytranslating a head-stack assembly (HSA) in a hard disk drive (HDD) toaccess multiple magnetic-recording disks, according to an embodiment.

DESCRIPTION

Approaches to a multi-disk hard disk drive having an actuator elevatormechanism are described. In the following description, for the purposesof explanation, numerous specific details are set forth in order toprovide a thorough understanding of the embodiments of the inventiondescribed herein. It will be apparent, however, that the embodiments ofthe invention described herein may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to avoid unnecessarily obscuring theembodiments of the invention described herein.

Physical Description of an Illustrative Operating Context

Embodiments may be used in the context of a multi-disk, reducedread-write head, digital data storage device (DSD) such as a hard diskdrive (HDD). Thus, in accordance with an embodiment, a plan viewillustrating a conventional HDD 100 is shown in FIG. 1 to aid indescribing how a conventional HDD typically operates.

FIG. 1 illustrates the functional arrangement of components of the HDD100 including a slider 110 b that includes a magnetic read-write head110 a. Collectively, slider 110 b and head 110 a may be referred to as ahead slider. The HDD 100 includes at least one head gimbal assembly(HGA) 110 including the head slider, a lead suspension 110 c attached tothe head slider typically via a flexure, and a load beam 110 d attachedto the lead suspension 110 c. The HDD 100 also includes at least onerecording medium 120 rotatably mounted on a spindle 124 and a drivemotor (not visible) attached to the spindle 124 for rotating the medium120. The read-write head 110 a, which may also be referred to as atransducer, includes a write element and a read element for respectivelywriting and reading information stored on the medium 120 of the HDD 100.The medium 120 or a plurality of disk media may be affixed to thespindle 124 with a disk clamp 128.

The HDD 100 further includes an arm 132 attached to the HGA 110, acarriage 134, a voice-coil motor (VCM) that includes an armature 136including a voice coil 140 attached to the carriage 134 and a stator 144including a voice-coil magnet (not visible). The armature 136 of the VCMis attached to the carriage 134 and is configured to move the arm 132and the HGA 110 to access portions of the medium 120, all collectivelymounted on a pivot shaft 148 with an interposed pivot bearing assembly152. In the case of an HDD having multiple disks, the carriage 134 maybe referred to as an “E-block,” or comb, because the carriage isarranged to carry a ganged array of arms that gives it the appearance ofa comb.

An assembly comprising a head gimbal assembly (e.g., HGA 110) includinga flexure to which the head slider is coupled, an actuator arm (e.g.,arm 132) and/or load beam to which the flexure is coupled, and anactuator (e.g., the VCM) to which the actuator arm is coupled, may becollectively referred to as a head stack assembly (HSA). An HSA may,however, include more or fewer components than those described. Forexample, an HSA may refer to an assembly that further includeselectrical interconnection components. Generally, an HSA is the assemblyconfigured to move the head slider to access portions of the medium 120for read and write operations.

With further reference to FIG. 1, electrical signals (e.g., current tothe voice coil 140 of the VCM) comprising a write signal to and a readsignal from the head 110 a, are transmitted by a flexible cable assembly(FCA) 156 (or “flex cable”). Interconnection between the flex cable 156and the head 110 a may include an arm-electronics (AE) module 160, whichmay have an on-board pre-amplifier for the read signal, as well as otherread-channel and write-channel electronic components. The AE module 160may be attached to the carriage 134 as shown. The flex cable 156 may becoupled to an electrical-connector block 164, which provides electricalcommunication, in some configurations, through an electricalfeed-through provided by an HDD housing 168. The HDD housing 168 (or“enclosure base” or “baseplate” or simply “base”), in conjunction withan HDD cover, provides a semi-sealed (or hermetically sealed, in someconfigurations) protective enclosure for the information storagecomponents of the HDD 100.

Other electronic components, including a disk controller and servoelectronics including a digital-signal processor (DSP), provideelectrical signals to the drive motor, the voice coil 140 of the VCM andthe head 110 a of the HGA 110. The electrical signal provided to thedrive motor enables the drive motor to spin providing a torque to thespindle 124 which is in turn transmitted to the medium 120 that isaffixed to the spindle 124. As a result, the medium 120 spins in adirection 172. The spinning medium 120 creates a cushion of air thatacts as an air-bearing on which the air-bearing surface (ABS) of theslider 110 b rides so that the slider 110 b flies above the surface ofthe medium 120 without making contact with a thin magnetic-recordinglayer in which information is recorded. Similarly in an HDD in which alighter-than-air gas is utilized, such as helium for a non-limitingexample, the spinning medium 120 creates a cushion of gas that acts as agas or fluid bearing on which the slider 110 b rides.

The electrical signal provided to the voice coil 140 of the VCM enablesthe head 110 a of the HGA 110 to access a track 176 on which informationis recorded. Thus, the armature 136 of the VCM swings through an arc180, which enables the head 110 a of the HGA 110 to access varioustracks on the medium 120. Information is stored on the medium 120 in aplurality of radially nested tracks arranged in sectors on the medium120, such as sector 184. Correspondingly, each track is composed of aplurality of sectored track portions (or “track sector”) such assectored track portion 188. Each sectored track portion 188 may includerecorded information, and a header containing error correction codeinformation and a servo-burst-signal pattern, such as anABCD-servo-burst-signal pattern, which is information that identifiesthe track 176. In accessing the track 176, the read element of the head110 a of the HGA 110 reads the servo-burst-signal pattern, whichprovides a position-error-signal (PES) to the servo electronics, whichcontrols the electrical signal provided to the voice coil 140 of theVCM, thereby enabling the head 110 a to follow the track 176. Uponfinding the track 176 and identifying a particular sectored trackportion 188, the head 110 a either reads information from the track 176or writes information to the track 176 depending on instructionsreceived by the disk controller from an external agent, for example, amicroprocessor of a computer system.

An HDD's electronic architecture comprises numerous electroniccomponents for performing their respective functions for operation of anHDD, such as a hard disk controller (“HDC”), an interface controller, anarm electronics module, a data channel, a motor driver, a servoprocessor, buffer memory, etc. Two or more of such components may becombined on a single integrated circuit board referred to as a “systemon a chip” (“SOC”). Several, if not all, of such electronic componentsare typically arranged on a printed circuit board that is coupled to thebottom side of an HDD, such as to HDD housing 168.

References herein to a hard disk drive, such as HDD 100 illustrated anddescribed in reference to FIG. 1, may encompass an information storagedevice that is at times referred to as a “hybrid drive”. A hybrid driverefers generally to a storage device having functionality of both atraditional HDD (see, e.g., HDD 100) combined with solid-state storagedevice (SSD) using non-volatile memory, such as flash or othersolid-state (e.g., integrated circuits) memory, which is electricallyerasable and programmable. As operation, management and control of thedifferent types of storage media typically differ, the solid-stateportion of a hybrid drive may include its own corresponding controllerfunctionality, which may be integrated into a single controller alongwith the HDD functionality. A hybrid drive may be architected andconfigured to operate and to utilize the solid-state portion in a numberof ways, such as, for non-limiting examples, by using the solid-statememory as cache memory, for storing frequently-accessed data, forstoring I/O intensive data, and the like. Further, a hybrid drive may bearchitected and configured essentially as two storage devices in asingle enclosure, i.e., a traditional HDD and an SSD, with either one ormultiple interfaces for host connection.

Introduction

References herein to “an embodiment”, “one embodiment”, and the like,are intended to mean that the particular feature, structure, orcharacteristic being described is included in at least one embodiment ofthe invention. However, instance of such phrases do not necessarily allrefer to the same embodiment,

The term “substantially” will be understood to describe a feature thatis largely or nearly structured, configured, dimensioned, etc., but withwhich manufacturing tolerances and the like may in practice result in asituation in which the structure, configuration, dimension, etc. is notalways or necessarily precisely as stated. For example, describing astructure as “substantially vertical” would assign that term its plainmeaning, such that the sidewall is vertical for all practical purposesbut may not be precisely at 90 degrees.

While terms such as “optimal”, “optimize”, “minimal”, “minimize”, andthe like may not have certain values associated therewith, if such termsare used herein the intent is that one of ordinary skill in the artwould understand such terms to include affecting a value, parameter,metric, and the like in a beneficial direction consistent with thetotality of this disclosure. For example, describing a value ofsomething as “minimal” does not require that the value actually be equalto some theoretical minimum (e.g., zero), but should be understood in apractical sense in that a corresponding goal would be to move the valuein a beneficial direction toward a theoretical minimum.

Recall that there is an increasing need for cost effective “active”archival storage (also referred to as “cold storage”), preferably havinga conventional form factor and utilizing many standard components. Oneapproach involves a standard HDD form factor (e.g., a 3.5″ form factor)and largely common HDD architecture, with a non-zero finite number of ndisks in one rotating disk stack, but containing fewer than 2nread-write heads, according to embodiments. Such a storage device mayutilize an articulation mechanism that can move the heads to mate withthe different disk surfaces (for a non-limiting example, only 2 headsbut 5+ disks for an air drive or 8+ disks for a He drive), where theprimary cost savings may come from eliminating the vast majority of theheads in the drive.

For a cold storage data storage device, a very thin structure (e.g., theread-write head stack assembly, or “HSA”) needs to be moved whilekeeping perpendicular to the axis on which it is moving. That structurealso needs to maintain sufficient stiffness for structural and resonancecontrol. There may be ball screws on the market that may comply withsuch requirements, but they are taller than the shaft they ride on andare typically considerably expensive.

With other possible approaches, there is a concern that when theactuator arms are unlocked during the time they need to be moved up anddown to get to different disks, the interface between the arms and thecam rattles or is relatively loose. This could cause undesirable motionin the suspensions and heads as the arms are raised and lowered. Thereis also a large range of potential friction between the cam threads, armthreads, and lock nut threads that could over time cause extra wear andbad repeatability in the vertical positioning achieved.

Actuator Subsystem for Reduced-Head Hard Disk Drive

FIG. 2A is a perspective view illustrating an actuator subsystem in areduced-head hard disk drive (HDD), FIG. 2B is an isolated perspectiveview illustrating the actuator subsystem of FIG. 2A, and FIG. 2C is anisolated plan view illustrating the actuator subsystem of FIG. 2A, allaccording to embodiments. FIGS. 2A-2C collectively illustrate anactuator subsystem comprising a low profile ball screw cam assembly 202(or “cam 202”), which transforms rotary motion into linear motion, witha stepper motor 204 (or “stepping motor”) disposed therein to form anactuator elevator subassembly, which is disposed within the actuatorpivot and pivot bearing of the actuator subsystem (e.g., the “pivotcartridge”) and is configured to vertically translate at least oneactuator arm 205 (see, e.g., arm 132 of FIG. 1) along with a respectiveHGA 207 (see, e.g., HGA 110 of FIG. 1). According to an embodiment, theactuator subsystem for a reduced-head HDD consists of two actuator arm205 assemblies each with a corresponding HGA 207 (e.g., a modified HSA,in which the actuator arm assemblies translate vertically, or elevate,while the VCM coil 209 may be fixed in the vertical direction) housing acorresponding read-write head 207 a (see, e.g., read-write head 110 a ofFIG. 1). Generally, the term “reduced-head HDD” is used to refer to anHDD in which the number of read-write heads is less than the number ofmagnetic-recording disk media surfaces.

With respect to electrical signal transmission, FIGS. 2A-2C furtherillustrate a flexible cable assembly 208 (“FCA 208”), which isconfigured to comprise a dynamic vertical “loop” 208 a (“FCA verticalloop 208 a”) for vertical translation of the end(s) that are coupled tothe actuator elevator subassembly and/or another portion of the actuatorsubsystem. This FCA vertical loop 208 a is in addition to a typicaldynamic horizontal loop for horizontal translation purposes for when theactuator to which one end is connected is rotating. The actuatorsubsystem further comprises at least one connector housing 210 forhousing an electrical connector for transferring electrical signals(e.g., motor power, sensor signals, etc.) between the actuator elevatorsubassembly and a ramp elevator assembly (described in more detailelsewhere herein).

With respect to actuator arm locking, FIGS. 2A-2C further illustrate anarm lock subsystem 206, coupled with or constituent to a coil supportassembly 212, configured to mechanically interact with an outer diametercrash stop 211 (“ODCS 211”) to lock and unlock the actuator elevatorsubassembly, as described in more detail elsewhere herein.

Actuator Elevator Assembly

FIG. 3 is a cross-sectional side view illustrating an actuator elevatorassembly, according to an embodiment. The actuator elevator assembly 300illustrated in FIG. 3 is configured for use in an actuator subsystem asillustrated and described in reference to FIGS. 2A-2C, i.e., configuredto vertically translate at least one actuator arm 205 (shown here is aportion of the arm 205 that engages with the pivot; see, e.g., FIGS.2A-2C, 4A-4C) with a respective HGA 207 (FIGS. 2B, 2C) and read-writehead 207 a (FIGS. 2B, 2C).

Actuator elevator assembly 300 comprises the actuator elevatorsubassembly comprising the ball screw cam 202, having the stepper motor204 coupled to (e.g., with an outer sleeve adhered to the inner surfaceof the cam 202) and disposed therein and interposed between the cam 202and a pivot shaft 310, where the pivot shaft 310 bottom is shownpositioned within an opening of a bottom support plate 308 b and thepivot shaft 310 top is shown positioned approaching or within an openingof a top support plate 308 a. In a typical HDD configuration, the innerpivot shaft 310 is further coupled to an HDD enclosure base (see, e.g.,housing 168 of FIG. 1) via a screw or other fastener and to an HDD cover(not shown) via another screw or fastener, effectively sandwiching thepivot shaft 310 and the actuator elevator assembly 300 more broadlywithin the corresponding HDD.

Actuator elevator assembly 300 further comprises a first set or pair ofHSA pivot bearings 302 (along with upper inner bearing housing 302 a andlower inner bearing housing 302 b) interposed between the pivot shaft310 and the stepper motor 204 (e.g., one bearing assembly near the topand one bearing assembly near the bottom). HSA pivot bearings 302function to support loads associated at least in part with the rotationof the actuator arms 205 (FIGS. 2A-2C), along with the stepper motor 204and the cam 202 to which it is attached, about the stationary pivotshaft 310, such as during actuator seek/read/write/load/unloadoperations. Actuator elevator assembly 300 further comprises a secondset or pair of cam bearings 304 interposed between the stepper motor 204and the cam 202 (e.g., one bearing assembly near the top and one bearingassembly near the bottom). Cam bearings 304 function to support loadsassociated at least in part with the rotation of the stepper motor 204and the cam 202 about the stationary pivot shaft 310 (when the actuatorelevator subassembly is decoupled from the HSA pivot inner bearinghousing 302 a, 302 b, as described in more detail elsewhere herein withrespect to the operation of the arm lock subsystem 206), such as duringactuator vertical translation operations.

Actuator elevator assembly 300 further comprises a third set of ballscrew bearings comprising balls 202 c and retainer 202 b interposedbetween a cam screw 202 a (see, e.g., FIGS. 4A-4C) and the actuator arm205. This ball screw bearing assembly functions to support loadsassociated at least in part with the rotation of the stepper motor 204and the cam 202 about the stationary pivot shaft 310 and the consequentactuator vertical translation operations.

Low Profile Ball Screw Cam

According to an embodiment, one approach to an actuator elevatormechanism for a cold storage HDD uses a multi-start threaded shaft (alsoreferred to as a “multi-start ball screw”) with a ball in each start tocreate a plane perpendicular to the screw/cam. The balls are heldequally spaced around the shaft by a bearing retainer. The balls arepreloaded to the shaft at all times by compressing the two outer races.This platform is stable and does not rattle or function loosely, thusproviding consistent structural integrity.

FIG. 4A is an exploded view illustrating a low-profile ball screw camassembly, and FIG. 4B is a partial cross-sectional view illustrating aportion of the cam assembly of FIG. 4A, according to an embodiment. Theillustrated ball screw cam assembly referred to as cam 202 comprises thehollow threaded shaft or screw 202 a, a bearing retainer 202 b orretaining ring with a plurality of equally-spaced retained balls 202 c,a bearing half-race 202 d, an O-ring 202 e, and, optionally, a C-clip202 f, according to an embodiment. Cam 202 is configured for use in theactuator elevator assembly 300 illustrated in FIG. 3, which isconfigured for use in the actuator subsystem illustrated and describedin reference to FIGS. 2A-2C, i.e., to vertically translate at least oneactuator arm 205 with a respective HGA 207 and read-write head 207 a.However, use of a cam mechanism such as cam 202 in implementationsoutside of such an actuator subsystem (e.g., in a camera, or in otherproducts requiring a miniature cam/translation mechanism) iscontemplated, so the use scenarios for cam 202 are not limited toimplementations only within such an actuator subsystem.

It is noteworthy that with cam 202, according to an embodiment, thenumber of starts equals the number of balls, thereby providing a stableplanar “platform” with a single bearing assembly and perpendicular tothe axis/translation path. According to an embodiment, three balls 202 care held within the bearing retainer 202 b, thereby providing a 3-pointplanar bearing assembly while facilitating the low-profile aspect of thecam 202. While three balls are needed to define or construct the plane,the number of balls 202 c may vary from implementation toimplementation. While greater than three balls 202 c provides a morestable planar platform (e.g., more contact points about the shaftprovides more actuator arm stiffness and stability), a greater number ofballs 202 c would also increase the thread pitch and lead correspondingto the screw thread (especially in view of a stepper motor driver),perhaps undesirably in some use scenarios.

With reference to FIG. 4B, one can see that the tapered starts/threadsof screw 202 a function as upper and lower portions of an inner race ofthe bearing assembly of cam 202. According to an embodiment, the outerrace of the bearing assembly of cam 202 is a split-race, i.e., a 2-partrace (whereby the two outer load surfaces are split among two parts),comprising a tapered inner surface 205 a of the opening in arm 205 as alower outer race surface, and a tapered lower surface of bearinghalf-race 202 d as an upper outer race surface, together forming whatmay be referred to as a v-notch outer race. The bearing assembly istherefore preloaded radially at four points of contact via the inner andouter races, while the O-ring 202 e (e.g., elastomeric) functions as aspring to provide a variable compression force applied to the bearinghalf-race 202 d, in conjunction with the C-clip 202 f Alternatively touse of an elastomeric O-ring 202 e (e.g., which can degrade and causecreep over time), according to an embodiment a wavy washer, functioningas a metallic spring, may be implemented to provide the compressionforce to the outer race. Hence, this arrangement functions to manage orcompensate for the possibility of slight changes in the diameter of theinner race/threads at various locations along the length of the screw202 a, such as those associated with part tolerances and manufacturingvariability.

Furthermore, one could eliminate use of the C-clip 202 f and reconfigurethe outer race, as illustrated in FIG. 4C. FIG. 4C is a partialcross-sectional view illustrating a portion of an alternative camassembly, according to an embodiment. As with the embodiment illustratedin FIG. 4B, the tapered starts/threads of screw 202 a function as upperand lower portions of an inner race of the bearing assembly of thisembodiment of ball screw cam, cam 203. Here also the outer race of thebearing assembly of cam 203 is a split-race, or 2-part race, comprisinga tapered half-race 202 d-1 as a lower outer race surface and a taperedhalf-race 202 d-2 as an upper outer race surface (bonded to an innersurface of the opening in arm 205 after preloading), together formingwhat may be referred to as a v-notch outer race. Here also the bearingassembly is therefore preloaded radially at four points of contact viathe inner and outer races, while the O-ring 202 e (or wavy washer)functions as a spring to provide a variable compression force applied tothe bearing split-race comprising 202 d-1, 201 d-2.

In-Pivot Claw-Pole Stepper Motor

In the context of a cold storage HDD that includes a rotary cam (e.g.,cam 202) that is rotated with respect to the coil assembly (e.g., VCMcoil 209), which would vertically move the actuator arms 205 up and downfrom disk to disk, a means to provide that rotation is needed. Accordingto an embodiment and with reference to FIGS. 2A-3, a stepper motor 204is assembled within the pivot (or, the pivot cartridge) of the actuatorsubsystem (FIGS. 2A-2C), which, in conjunction with the cam 202 (FIGS.4A-4B), forms an actuator elevator assembly 300 (FIG. 3).

So-called “claw-pole” designs contain an inner permanent magnet (PM)mounted on a rotary lead-screw shaft. In the context of a multi-disk HDDhaving an actuator elevator mechanism, the actuator subsystem designcomprises a stationary shaft during the translation of the head stackassembly (HSA) to switch between magnetic recording disks. With this, aunique design of a claw-pole stepper motor is needed. The smaller magnetvolume of a typical claw-pole motor where the stator circumscribes thePM requires a high number of turns (100 or more) with a very smallcopper wire (e.g. 0.05 millimeter (mm)) due to the physical limitations.Because electromagnetic torque, T_(e)=kD²L, is proportional to thesquare of the diameter of the magnetic air gap and the stator stacklength, it is advantageous to maximize the motor diameter.

However, winding with a smaller wire diameter is difficult due to itsfragility and is more susceptible to the fluctuation of the windingtension that causes wider distribution of the winding resistance. A highnumber of turns with a small diameter wire results in a higher copperloss, P_(copper loss)=i²R, and subsequent heat that may adversely affectthe internal environment of the HDD in terms of the dynamic read-writehead gap due to potential ball-bearing oil migration. Thus, in theconfined space of the cold storage data storage device rotary cam, it ispreferable to implement a compact stepper motor to rotate the cam inorder to move the HSA bi-directionally in the vertical direction toaccess different disks in the stack.

A claw-pole motor such as stepper motor 204 comprises, for example, twouni-filar windings in injection-molded-plastic spools for bipolarcontrol and four claw-pole stators made from cold-rolled steel sheetmetal, electrical steel sheet metal, SMC (Soft Magnetic Composite), andthe like, where use of electrical steel with various levels of siliconcontent or SMC reduces the eddy current loss. Furthermore, use of SMCcan produce a complex geometry through powder metallurgy, unlike stampedand formed electrical steel sheet. Each stator contains p/2 teeth(p=number of poles) (e.g., 5 teeth per claw-pole stator according to anembodiment of stepper motor 204 having a 10-pole PM). The step angle ofa stepper motor depends on the number of poles and stator teeth. In adesign having 10 poles and 20 teeth, suitable for the intended purpose,the step angle/rotation is 18° or 20 steps/revolution in a full-stepcontrol, with both stator assemblies having a pair of claw-pole statorsshifted relative to the other by one-half pole width, and where the stepangle is inversely proportional to the number of stator teeth. Likewise,a design with 100 teeth yields 360°/100 or 3.6°/step angle, for example.In the case of 4 start-threaded rotary cam, this 3.6° step angle wouldprovide 4 mm/100 steps or 0.04 mm step resolution rather than 4 mm/20steps or 0.2 mm step resolution, thus providing a more precise andaccurate servo control for positioning the HSA between the disks. Statedotherwise, a higher number of the claw (stator) teeth provides for asmaller step resolution. However, the outer diameter (OD) of the system(e.g., cam 202) limits the possible number of claw teeth. That is, witha given OD there is a practical limit to the number of teeth implementedbecause adding more teeth reduces their size and leads to manufacturingdifficulty, magnetic saturation, and unstable tooth structures. Forexample, with an 18 mm OD, the system could be limited to 40 teeth and astep angle of 360°/40 or 9°. To get a higher step resolution, amicro-step may be used, where a typical bi-polar driver provides ½, ¼,⅛, 1/16, and 1/32 micro-steps.

A corresponding rotor of stepper motor 204 comprises a PM (e.g. Nd—Fe—B)attached to the inner diameter of the cam 202 (see, e.g., FIG. 3),which, according to an embodiment, is constructed of ferritic stainlesssteel, and where the PM comprises 10 hetero-polar magnets. Hence, whenthe coils are energized the teeth become north and south poles, andmutual torque is established when the north PM poles align with thesouth claw poles and the south PM poles align with the north claw poles.Reversing the current polarity in the stator coils reverses the polarityof the electromagnetic claw poles and the resultant torque advances therotor one full step.

Note that the number of coils and corresponding claw-pole stator pairs(i.e., phases), and the number of corresponding teeth on each claw-polestator, may vary from implementation to implementation based on specificdesign goals (e.g., torque, phases and rotational degrees/step orsteps/revolution) and, therefore, are not limited by the numberdescribed in the foregoing example. For example, with a 2-inchform-factor HDD, a four-coil design is feasible, which equates to 9°step angle, i.e., 360°/(number of teeth per claw)*(number ofclaws)=360°/(4*10)=9°/step. Alternatively, the step angle can becomputed from the corresponding number of rotor poles and phases, i.e.,360°/(2 phases*20 rotor poles)=9°/step.

With reference back to FIG. 3, stepper motor 204 comprises a circular“phase A” coil 320 a (with or without corresponding bobbin) enveloped bya pair of corresponding circular and mating claw-poles stators 321 a, acircular “phase B” coil 320 b (with or without corresponding bobbin)enveloped by a pair of corresponding circular and mating claw-polestators 321 b, disposed within a circular permanent magnet 322 (“PM322”), all positioned around the stationary shaft 310. Note that whenthe HSA moves (e.g., actuator arm 205 seeks), the cam 202 and the HSApivot bearing 302 upper and lower housing 302 a, 302 b movesynchronously and thus eliminate the differential reluctance or coggingtorque that must be overcome in the rotary motion of the HSA.

According to an embodiment, it is noteworthy that in-pivot stepper motor204 is configured with an outer rotor and inner stators. That is, incontrast with typical stepper motors, here the PM 322 is on the outsideof the stepper motor 204 assembly and the claw-poles 321 a, 321 b andcoils 320 a, 320 b are on the inside of the PM 322. Likewise, while aconventional stepper motor typically rotates a central shaft, here theshaft 310 is fixed/stationary and the PM 322 rotor is bonded to theinner diameter of the cam shaft or screw 202 a such that the steppermotor 204 rotates the outer cam 202 about the fixed inner shaft 310. Inthat sense, this embodiment of stepper motor 204 is akin to aconventional stepper motor that is “turned inside-out”.

Method of Assembling an Actuator Elevator Subassembly

A method of assembling an actuator elevator subassembly, according to anembodiment, is as follows. The described method may be used to assemblean assembly comprising the cam 202 and a 10-pole stepper motor such asin-pivot stepper motor 204, for example. However, as described elsewhereherein, the number of poles may vary from implementation toimplementation and therefore, is not so limited.

First, insert the upper HSA pivot bearing 302 into the upper innerbearing housing 302 a and bond (e.g., glue) the outer race of the upperHSA pivot bearing 302 to the upper inner bearing housing 302 a. Next,insert the upper cam bearing 304 around the inner bearing housing 302 aand bond the inner race of the upper cam bearing 304 to the upper innerbearing housing 302 a. Once these bearings 302, 304 are assembled, themethod moves on to the stepper motor 204, as follows.

Insert around, orient, and bond a claw-pole stator 321 a (a first halfof a first pair) to an outer sleeve portion of the upper inner bearinghousing 302 a. Next, insert within and bond a first coil 320 a to thefirst claw-pole stator 321 a of the first pair. Next, rotate a claw-polestator 321 a (the second half of the first pair) 36° relative to thefirst claw-pole stator 321 a of the first pair and bond the second halfof the claw-pole stator 321 a to the outer sleeve portion of the upperinner bearing housing 302 a. Next, rotate a claw-pole stator 321 b (afirst half of a second pair) 18° relative to the second claw-pole stator321 a of the first pair and bond the first half of the claw-pole stator321 b of the second pair to the outer sleeve portion of the upper innerbearing housing 302 a. Next, insert around and bond a second coil 320 bto the upper inner bearing housing 302 a. Next, rotate a claw-polestator 321 b (the second half of the second pair) 36° relative to thefirst claw-pole stator 321 b of the second pair and bond the second halfof the claw-pole stator 321 b to the outer sleeve portion of the upperinner bearing housing 302 a. Insert a magnetized PM 322 (magnetized toproduce 10 pole, or 5 pole-pairs) and bond the outer diameter surface ofthe PM 322 to in the inner diameter surface of the screw 202 a. Once thestepper motor is assembled as above, the method moves on to the lowerbearings, as follows.

Insert the lower HSA pivot bearing 302 into the lower inner bearinghousing 302 b and bond the outer race of the lower HSA pivot bearing 302to the lower inner bearing housing 302 b. Next, insert the lower cambearing 304 around the lower inner bearing housing 302 b and bond theinner race of the lower cam bearing 304 to the lower inner bearinghousing 302 b. Next, bond the outer race of the lower cam bearing 304,now in assembly form with the lower HSA pivot bearing 302 and the lowerinner bearing housing 302 b, into the screw 202 a subassembly. Next,apply bonding adhesive completely around the outer diameter periphery ofthe upper inner bearing housing 302 a, and apply bonding adhesive to theouter race of the upper cam bearing 304, and insert this subassemblyinto the screw 202 a subassembly. Next, apply an adhesive bead to thelower inner bearing housing 302 b and insert that lower bearing assemblyinto the screw 202 a subassembly and the upper bearing subassembly.Finally, heat-cure the thermoset adhesive by placement of the assemblyin an oven, for example.

Locking/Unlocking Mechanism for Vertically Translatable ActuatorAssembly

FIG. 5A is a perspective view illustrating an actuator-elevatorassembly, FIG. 5B is a plan view illustrating the actuator-elevatorassembly of FIG. 5A, and FIG. 5C is a perspective view illustrating theactuator-elevator assembly of FIG. 5A in a reduced-head data storagedevice, all according to an embodiment. According to an embodiment andwith reference to FIGS. 2A-4B, the locking/unlocking mechanism isconstituent to the actuator subsystem (FIGS. 2A-2C) and which operatesto vertically lock the actuator arm in place during seek/read/writeoperations, for example, and to unlock the actuator arm for verticaltranslation under the control of the cam 202 (FIGS. 4A-4B) and thestepper motor 204 (FIGS. 2A-3) constituent to the actuator elevatorassembly 300 (FIG. 3).

FIGS. 5A-5C collectively illustrate a locking/unlocking mechanismpreviously-introduced as arm lock subsystem 206 (hereinafter, “lockingmechanism 206”), located in the general area labeled as B-B in FIG. 5A.Locking mechanism 206 comprises a tab 206 d extending from actuator arm205 into a slot 206 e within the structure of coil support assembly 212,whereby the tab 206 d is squeezed, held, locked within the slot 206 ewhen in a cam locked position and is released, unlocked from thecompression of the slot 206 e and therefore free to travel in thevertical direction when in a cam unlocked position. According to anembodiment, the tab 206 d and/or the clamping surfaces of the slot 206 eare coated with a low-wear, high-coefficient of friction material toprovide for strong clamping while inhibiting the undesirable particlegeneration within the drive. Locking mechanism 206 further comprises aspring mechanism 206 b disposed within a slit 206 c within the coilsupport assembly 212, wherein the slit 206 c intersects the slot 206 e.According to an embodiment, the spring mechanism 206 b is a sheet-likepiece of material that is relatively thin, and long in the verticaldirection in comparison with its width positioned coincident within theslit 206 c. The spring mechanism 206 b is rigid enough andconfigured/positioned within the slit 206 c spanning across the slot 206e such that the force produced by the spring mechanism 206 b, in alocked or default position (i.e., slightly bent along a vertical axis toelicit a spring-like force), compresses each side of the slot 206 etoward each other to squeeze and hold the tab 206 d in a fixed positionwithin the slot 206 e.

The cam is unlocked when the force associated with the spring mechanism206 b is overcome, thereby opening wider the slot 206 e, such that thetab 206 d is released from the hold of the slot 206 e and therebyenabled to travel vertically within the slot 206 e so that the actuatorarm 205 from which the tab 206 d extends can be vertically translated bythe actuator elevator assembly 300. The force of spring mechanism 206 bis overcome when a lock arm 206 a, which is part of or constituent tothe coil support assembly 212, and which is part of or extension of oneside of the slot 206 e, mechanically interacts with thepreviously-introduced ODCS 211, according to an embodiment.Alternatively, interaction with a mechanical element, feature, orstructure other than a crash stop could be used to overcome the holdingforce of the spring mechanism 206 b. As such, when the actuator arm 205is driven/rotated far enough past the outer diameter of the disk stack,the lock arm 206 a “crashes” into the ODCS 211, which causes the lockarm 206 a to rotate (e.g., counter-clockwise) which then functions toopen the gap corresponding to slot 206 e (e.g., similarly to how aclothes-pin functions).

Flexible Cable Assembly with Vertical Loop

FIG. 6A is an isolated perspective view illustrating an actuatorposition sensor and flexible cable assembly, and FIG. 6B is aperspective view illustrating the assembly of FIG. 6A assembled with theactuator elevator assembly of FIG. 3, both according to an embodiment.According to an embodiment and with reference to FIGS. 2A-5C, theillustrated actuator position sensor and flexible cable assembly areconstituent to the actuator subsystem (FIGS. 2A-2C), which provides forvertical translation of the actuator arm 205 under the control of thecam 202 (FIGS. 4A-4B) and the stepper motor 204 (FIGS. 2A-3) constituentto the actuator elevator assembly 300 (FIG. 3).

Conventional HDDs typically include a flexible cable assembly (FCA) suchas FCA 156 of FIG. 1, which require some slack in the horizontaldirection (e.g., XY direction) to allow for the distance between itsconnection points to vary in the horizontal direction in response toactuator rotation, as one connection point is with part of the actuatorarm. However, an FCA cable for a rotating and vertically translatingactuator connects to an actuator that not only moves in the XY plane forseeking data on the disk, but also moves in the Z direction to moveamong the disks in the multi-disk stack. Thus, a complete flex may bedesigned as either a one part solution or designed as two differentparts combined together, with the use of a connector to carry electricalsignals. With an actuator that is configured to move vertically, such asin the context of the actuator subsystem described in reference to ofFIGS. 2A-5C, according to an embodiment the FCA 208 (see, e.g., FIGS.2A-2C, not shown here), which moves in the XY direction such as duringseeking, further comprises or is electronically coupled or spliced witha dynamic vertical loop portion of FCA, referred to as FCA vertical loop208 a, which moves effectively independently of the FCA 208 portion suchas when the actuator is vertically translating. Functionally similar tothe FCA 156, the FCA vertical loop 208 a provides some slack in the Zdirection to allow for the distance between its connection points tovary in the vertical direction in response to actuator verticaltranslation, as one connection point is with part of the actuator arm205. Both the horizontal loop of FCA 208 and the FCA vertical loop 208 aare configured to move independently of the other.

Note that the configuration and shape of the FCA vertical loop 208 a mayvary from implementation to implementation. According to an embodiment,a “U-loop” configuration is implemented for FCA vertical loop 208 a (theloop generally resembles a letter “U” in various not-fully-extendedstates), as depicted in FIGS. 6A-6B. However, other shaped verticalloops may be designed and implemented for use in this context, such as aC-loop shape that resembles the letter “C” when not fully extended andan S-loop shape that resembles the letter “S” when not fully extended,and the like. In the configuration depicted, the FCA vertical loop 208 ais positioned near a preamp 606 and whereby the XY loop of FCA 208electrically connects the FCA vertical loop 208 a to a bracket and/or aconnector housing 210 (see, e.g., FIGS. 2A-2C).

Further illustrated in FIGS. 6A-6B is a pair of proximity or positionsensors 602 coupled to the actuator arm 205 and configured to sense theZ position of the actuator arm 205 (e.g., vertical height) relative to amagnetic encoding strip and, ultimately, relative to the disk stack.According to an embodiment, one or more Hall effect sensors mounted in aquadrature configuration are implemented for the position sensor(s) 602,which function in coordination with a closely-positioned magneticencoder strip 604, mounted on a stiffener 605, to provide sine andcosine signals for sensing the directions and crossing of the waveforms.The stiffener 605 may further function for positioning of the FCA 208and FCA vertical loop 208 a.

Generally, magnetic flux density in the air gap between the Hall sensorsand the permanent magnet scale (i.e., magnetic encoding strip 604)should be set at an optimum gap range to provide adequate signalstrength. A narrow gap causes signal saturation and a wide gap weakensthe signal. In either case, detection of the zero-crossing points isuncertain. However, the quadrature configuration of the Hall sensors inconjunction with a 1 mm pole-pitch magnetic scale provides displacementand direction simultaneous by virtue of the leading and lagging natureof the waveforms in the upward and downward translations. For example,one Hall sensor signal leads when the stepper motor moves downward, andanother Hall sensor signal leads when the stepper motor moves upward. Aleading Hall sensor signal indicates the translational direction and thezero-crossing points of the sine-cosine waveforms provide the amount ofthe displacement.

Alternative Actuator Subsystem for Reduced-Head Hard Disk Drive

In the context of a cold storage HDD that includes a rotary cam (e.g.,cam 202 of FIGS. 2A-5C) that is rotated with respect to an actuator coilassembly (e.g., VCM coil 209 of FIGS. 2B, 2C, 5A, 5B), which wouldvertically move a head-stack assembly (HSA) comprising one or moreactuator arms (e.g., actuator arm 205 of FIGS. 2A-2C, 4A-4C, 5A, 5B) upand down from disk to disk, a means to provide that rotation is needed.According to an embodiment and with reference to FIG. 7 (and FIGS.2A-2C), an axial flux permanent magnet (AFPM) motor 704 is assembledwith the pivot assembly of the actuator subsystem (FIGS. 2A-2C, 7),which, in conjunction with a cam 702 similar to or the same as the cam202 (FIGS. 4A-4B), forms an actuator elevator assembly similar toactuator elevator assembly 300 (FIG. 3), however with the AFPM motor 704substituted for a claw-pole stepper motor embodying stepper motor 204.

In the context of a multi-disk HDD having an actuator elevatormechanism, the actuator subsystem design comprises a stationary shaftduring the translation of the head stack assembly (HSA) to switchbetween magnetic recording disks. Furthermore, in the confined space ofreduced-head hard disk drive rotary cam, it is preferable to implement acompact motor to rotate the cam in order to move the HSAbi-directionally in the vertical direction to access different disks inthe stack. With this, a unique design of a motor is needed. Thus, anAFPM motor may be implemented alternatively to an in-pivot steppermotor, such as the claw pole stepper motor 204 (FIGS. 2A-3), to increasethe torque within similar radial and axial space constraints and todecrease heat generation while increasing heat dissipation within anearly enclosed space with very little air circulation and ventilation,for examples.

FIG. 7 is a perspective view illustrating an actuator subsystem in areduced-head hard disk drive, according to an embodiment. Actuatorsubsystem 700 comprises a low profile ball screw cam assembly 702 (or“cam 702”), which transforms rotary motion into linear motion whendriven by an axial flux permanent magnet (AFPM) motor 704 (or simply“AFPM motor 704”) coupled with a screw 702 a to form an actuatorelevator subassembly, which is configured to vertically translate atleast one actuator arm 705 (see, e.g., arm 132 of FIG. 1 and actuatorarm 205 of FIGS. 2A-2C, 4A-4C, 5A, 5B) along with a respective HGA 707(see, e.g., HGA 110 of FIG. 1). According to an embodiment, the actuatorsubsystem for a reduced-head HDD consists of two actuator arm 705assemblies, as depicted, each with a corresponding HGA 707 (e.g., amodified head-stack assembly (HSA) in which the actuator arm assembliestranslate vertically, or elevate, while the VCM coil 709 or voice coilmotor assembly (VCMA), collectively, may be fixed in the verticaldirection) housing a corresponding read-write head 707 a (see, e.g.,read-write head 110 a of FIG. 1). Generally, the term “reduced-head HDD”is used to refer to an HDD in which the number of read-write heads isless than the number of magnetic-recording disk media 720 surfaces.

Actuator Elevator Assembly Having Axial Flux Permanent Magnet Motor

FIG. 8 is a cross-sectional side view illustrating an actuator elevatorassembly including an “external” axial flux permanent magnet motor,according to an embodiment. This configuration of an actuator elevatorassembly is referred to as “external” because the motor is external tothe cam, generally, and the cam screw more particularly. The actuatorelevator assembly 800 is configured for use in an actuator subsystem asillustrated and described in reference to FIG. 7 (as well as an actuatorsubsystem as illustrated and described in reference to FIGS. 2A-2C),i.e., configured to vertically translate at least one actuator arm 705(see, e.g., a similar arm 205 of FIGS. 2A-2C, 4A-4C) with a respectiveHGA 707 (see, e.g., a similar HGA 207 FIGS. 2B, 2C) and read-write head707 a (see, e.g., a similar read-write head 207 a FIGS. 2B, 2C).

Actuator elevator assembly 800 comprises the actuator elevatorsubassembly comprising the ball screw cam 702 with the AFPM motor 704affixed thereto, as described in more detail elsewhere herein, andcollectively assembled around and configured to rotate about a pivotshaft 710. Here, the bottom of the pivot shaft 710 is shown positionedwithin a lower bearing assembly (e.g., HSA pivot bearing 802) and thetop of the pivot shaft 710 top is shown positioned within an upperbearing assembly (e.g., HSA pivot bearing 802). In a typical HDDconfiguration, the inner pivot shaft 710 is further coupled to an HDDenclosure base (see, e.g., housing 168 of FIG. 1) via a screw 820 orother fastener and to an HDD cover via another screw or fastener (notshown here), effectively sandwiching the pivot shaft 710 and theactuator elevator assembly 800 within the corresponding HDD.

Actuator elevator assembly 800 further comprises a first set or pair ofHSA pivot bearings 802 (e.g., one bearing assembly near the top and onebearing assembly near the bottom), along with upper inner bearinghousing 802 a and lower inner bearing housing 802 b, where the upperinner bearing housing 802 a is interposed at least in part between thepivot shaft 710 and the AFPM motor 704. HSA pivot bearings 802 functionto support loads associated at least in part with the rotation of theactuator arms 705, along with the AFPM motor 704 and the cam 702 towhich it is attached, about the stationary pivot shaft 710, such asduring actuator seek, read, write, load, unload operations (a lockedstatus). Actuator elevator assembly 800 further comprises a second setor pair of cam bearings 804 disposed within the cam 702 (e.g., onebearing assembly near the top and one bearing assembly near the bottom).Cam bearings 804 function to support loads associated at least in partwith the rotation of the AFPM motor 704 and the cam 702 about thestationary pivot shaft 710, such as when the actuator elevatorsubassembly 800 is unlocked or decoupled from the HSA pivot bearings802, such as during actuator vertical translation operations along thelength of the cam screw 702 a.

According to an embodiment, actuator elevator assembly 800 furthercomprises a third set of ball screw bearings, as illustrated anddescribed in reference to FIGS. 4A-4C, comprising balls 202 c andretainer 202 b interposed between a cam screw 202 a (or cam screw 702 a)and the actuator arm 205 (or actuator arm 705). This ball screw bearingassembly functions to support loads associated at least in part with therotation of the AFPM motor 704 and the cam 702 about the stationarypivot shaft 710 and the consequent actuator arm 205, 705 verticaltranslation operations.

According to an embodiment, the cam screw 702 a of the actuator elevatorassembly 800 further comprises an upper flange 810 to which anaxially-magnetized permanent magnet (PM) 812 a (e.g., composed ofNd—Fe—B) rotor 812 of the AFPM motor 704 is affixed. As depicted in FIG.8, the upper flange 810 and the rotor 812 are both annular pieces,positioned around the outer diameter of the upper inner bearing housing802 a of upper HSA bearing assembly 802. Thus, the “back-iron” for theaxial PM 812 a ring is, as upper flange 810, an extension of the camscrew 702 a and thereby reduces the need for additional vertical space.According to an embodiment, the cam screw 702 a and the upper flange 810thereof are constructed, composed, fabricated from a ferritic (e.g.,magnetic) stainless steel such as DHS9 (a lead-free material), forstrength, dimensional stability, and magnetic permeability.

According to an embodiment, the AFPM motor 704 of the actuator elevatorassembly 800 further comprises a stator 814, comprising an integratedstator-top bracket assembly comprising a top bracket 814 a of theactuator elevator assembly 800, where the bracket 814 a comprises (i) aplurality of AFPM motor stator cores 814 b (or “core protrusions 814 b”)extending therefrom, and (ii) a plurality of AFPM motor stator coils 814c each wound around a corresponding one of the core protrusions 814 b.Thus, the AFPM motor stator 814 is fabricated as an integral part of thetop bracket 814 a of the actuator elevator assembly 800, therebyreducing the use of the premium vertical space associated with a lowprofile ball screw cam 702 of actuator subsystem 700 (FIG. 7). Accordingto an embodiment, the top bracket 814 a is constructed, composed,fabricated from a soft magnetic composite (SMC) material, which enablesthe molding of complex shapes in powder metal sintering process where aprogressive-die stamping and forming processs may become impractical.Unlike the limitations of the electrical-steel laminations, the SMCenables the design of magnetic circuits in 3D flux paths to achievecomplex and compact topology. According to an alternative embodiment,the top bracket 814 a is constructed, composed, fabricated from aferritic stainless steel such as DHS9.

FIG. 9 is a cross-sectional side view illustrating a portion of anactuator elevator mechanism including an “internal” axial flux permanentmagnet motor, according to an embodiment. This configuration of anactuator elevator assembly is referred to as “internal” because themotor is positioned internally or disposed within the cam, generally,and the cam screw more particularly. The actuator elevator assembly 900is configured for use in an actuator subsystem as illustrated anddescribed in reference to FIG. 7 (as well as an actuator subsystem asillustrated and described in reference to FIGS. 2A-2C), i.e., configuredto vertically translate at least one actuator arm 705 (see, e.g., asimilar arm 205 of FIGS. 2A-2C, 4A-4C) with a respective HGA 707 (see,e.g., a similar HGA 207 FIGS. 2B, 2C) and read-write head 707 a (see,e.g., a similar read-write head 207 a FIGS. 2B, 2C).

Actuator elevator assembly 900 comprises an actuator elevatorsubassembly comprising a ball screw cam 902 (similar to but altered fromthe configuration of cam 702 of FIGS. 7-8) with an AFPM motor 904affixed thereto, as described in more detail elsewhere herein, andcollectively assembled around and configured to rotate about a pivotshaft 710. Here, the bottom of the pivot shaft 710 is shown positionedwithin a lower bearing assembly (e.g., HSA pivot bearing 903) and thetop of the pivot shaft 710 top is shown positioned within an upperbearing assembly (e.g., HSA pivot bearing 903). In a typical HDDconfiguration, the inner pivot shaft 710 is further coupled to an HDDenclosure base (see, e.g., housing 168 of FIG. 1) via a screw 820 orother fastener and to an HDD cover via another screw or fastener (notshown here), effectively sandwiching the pivot shaft 710 and theactuator elevator assembly 900 within the corresponding HDD.

Actuator elevator assembly 900 further comprises a first set or pair ofHSA pivot bearings 903 (e.g., one bearing assembly near the top and onebearing assembly near the bottom), along with upper inner bearinghousing 903 a and lower inner bearing housing 903 b. HSA pivot bearings903 function to support loads associated at least in part with therotation of the actuator arms 705, along with the AFPM motor 904 and thecam 902 to which it is attached, about the stationary pivot shaft 710,such as during actuator seek, read, write, load, unload operations (alocked status). Actuator elevator assembly 900 further comprises asecond set or pair of cam bearings 905 disposed within the cam 902(e.g., one bearing assembly near the top and one bearing assembly nearthe bottom). Cam bearings 905 function to support loads associated atleast in part with the rotation of the AFPM motor 904 and the cam 902about the stationary pivot shaft 710, such as when the actuator elevatorsubassembly 900 is unlocked or decoupled from the HSA pivot bearing 903,such as during actuator vertical translation operations along the lengthof the cam screw 902 a.

According to an embodiment, actuator elevator assembly 900 furthercomprises a third set of ball screw bearings, as illustrated anddescribed in reference to FIGS. 4A-4C, comprising balls 202 c andretainer 202 b interposed between a cam screw 202 a (or cam screw 902 a)and the actuator arm 205 (or actuator arm 705). This ball screw bearingassembly functions to support loads associated at least in part with therotation of the AFPM motor 904 and the cam 902 about the stationarypivot shaft 710 and the consequent actuator arm 205, 705 verticaltranslation operations.

According to an embodiment, the cam screw 902 a of the cam 902 of theactuator elevator assembly 900 comprises an annular step structure 910(or “step 910”) extending radially inward from the inner diameter of thecam screw, and to which an annular axially-magnetized permanent magnet(PM) 912 a (e.g., composed of Nd—Fe—B) rotor 912 is affixed (glued, forexample). As depicted in FIG. 9, the rotor 912 is an annular piece,positioned around the shaft 710. According to an embodiment, the camscrew 902 a is constructed, composed, fabricated from a ferriticstainless steel such as DHS9.

According to an embodiment, the AFPM motor 904 of the actuator elevatorassembly 900 further comprises a stator 914, comprising a plurality ofAFPM motor stator cores 914 b (or “core protrusions 914 b”) and aplurality of AFPM motor stator coils 914 c each wound around acorresponding one of the core protrusions 914 b. According to anembodiment, actuator elevator assembly 900 further comprises a bearingsleeve or bearing housing 903 c coupled with and extending from theupper inner bearing housing 903 a of HSA pivot bearing 903 to or towardthe lower inner bearing housing 903 b of HSA pivot bearing 903. Thestator 914 (including the core protrusions 914 b and coils 914 c) of theAFPM motor 904 is mounted or affixed to the outer diameter of thebearing housing 903 c, such as glued to a stator support structure 913.Thus, with the AFPM motor 904 installed internally to the cam screw 902a of actuator elevator assembly 900, the vertical space associated witha low profile ball screw cam 702 of actuator subsystem 700 (FIG. 7) canbe reduced even more significantly than with the external AFPM motor 804of actuator elevator assembly 800 (FIG. 8).

Axial Flux Permanent Magnet (AFPM) Motor

An AFPM (axial flux permanent magnet) motor (also referred to as“pancake” motor) is a geometry of motor construction in which the gapbetween the rotor and stator, and therefore the direction of magneticflux between the two, is aligned parallel with the axis of rotationrather than radially as with the concentric cylindrical geometry of themore common radial gap motor. Generally, an AFPM motor can providegreater electromagnetic torque relative to any conventional RFPM (RadialFlux Permanent Magnet) motor, for a given electromagnetic volume (e.g.,considering the stack length of the stator and the mean diameter of theair gap).

FIG. 10A is an exploded view of an axial flux permanent magnet motor,and FIG. 10B is another exploded view of the axial flux permanent magnetmotor of FIG. 10A, both according to an embodiment. The AFPM motorillustrated in FIGS. 10A-10B is an example implementation of the AFPMmotor 804 of the actuator elevator assembly 800 of FIG. 8. As discussed,AFPM motor 804 comprises a rotor 812 comprising an axially-magnetizedannular permanent magnet (PM) 812 a (e.g., composed of Nd—Fe—B), whichis configured for attachment to a mounting structure such as the upperflange 810 (FIG. 8) of the cam screw 702 a (FIGS. 7-8). According to aparticular but non-limiting embodiment, a compression-molded Nd—Fe—B PM812 a has a thickness of 0.6 mm and is magnetized axially to have either12 poles (6 pole pairs) or 16 pole (8 pole pairs) to work with 9 statorsalient poles or 12 stator salient poles, respectively. AFPM motor 804further comprises a stator 814 which, according to an embodiment,comprises the integrated stator-top bracket assembly. As discussed, suchan assembly comprises the top bracket 814 a of the actuator elevatorassembly 800 (FIG. 8), where the bracket 814 a includes the plurality ofAFPM motor stator core protrusions 814 b (only some of which are labeledhere, for drawing simplicity and clarity) extending therefrom, and theplurality of AFPM motor stator coils 814 c (only some of which arelabeled here, for drawing simplicity and clarity) each wound around acorresponding one of the core protrusions 814 b. Thus, with thisembodiment, the AFPM motor stator 814 is fabricated as an integral partof the top bracket 814 a of the actuator elevator assembly 800. Thenumber of turns and wire gage for the stator coils 814 c can be designedand optimized for a specific electromangetic torque to meet the productminimum requirements according to the electric and magnetic loadings.

Method for Translating a Head-Stack Assembly to Access Multiple Disks

FIG. 11 is a flow diagram illustrating a method for verticallytranslating a head-stack assembly (HSA) in a hard disk drive (HDD) toaccess multiple magnetic-recording disks, according to an embodiment.FIG. 11 is described in further reference to components illustrated inFIGS. 7-10B and, as discussed elsewhere herein, AFPM motor 704, 904 maybe assembled with and operate in conjunction with cam 702, 902, e.g.,functionally similar to the cam 202 of FIGS. 2A-3 and structurallysimilar to the cam 202 and associated sub-components of FIGS. 4A-4C, andmay be implemented in an assembly as depicted in FIGS. 5A-5C. That is,the AFPM motor 704, 904 may be implemented similarly to (e.g.,substituted for functionally and operationally) the stepper motor 204 ofFIG. 3 and the corresponding applications, implementations, andinstallations described in reference thereto.

At block 1102, an axial flux permanent magnet (AFPM) motor that isaffixed to a screw of a ball screw cam assembly is driven, to rotate thescrew about a coaxial (e.g., with the AFPM motor) shaft. For example,AFPM motor 704, 904 affixed to cam screw 702 a, 902 a of cam 702, 902 isdriven, e.g., by applying electrical current to the AFPM motor 704, 904thereby rotating the screw 702 a, 902 a of the cam 702, 902.

At block 1104, a planar multi-ball bearing assembly, which is coupledwith a hard disk drive (HDD) head-stack assembly (HSA) is allowed totranslate (e.g., vertically) in response to rotation of the screw. Forexample, driving the rotation of the screw 702 a, 902 a via the AFPMmotor 704, 904 drives translation of an HSA comprising one or moreactuator arms (e.g., actuator arm 205 of FIGS. 2A-2C, 4A-4C, 5A, 5B oractuator arm 705 of FIG. 7, coupled with the bearing balls 202 c andretainer 202 b of FIGS. 4A-4C) up and down from disk to disk along thelength of screw 702 a, 902 a. Thus, the read-write head(s) of the HSA isenabled to access and perform read operations and write operations oneach respective magnetic recording disk (e.g., disk medium 120 of FIG. 1or disk medium 720 of FIG. 7) of a multi-disk stack of a reduced-headHDD.

According to an embodiment, translation of the HSA includes translating(e.g., vertically) a multi-ball bearing assembly coupled with the HSA,by each of a particular number of balls of the bearing assembly ridingin a corresponding respective start of the same particular number ofstarts of the multi-start screw. For example, translation of the HSAincludes translating (e.g., vertically) actuator arms 705 (e.g., similarto actuator arm 205 of FIG. 4A) coupled with the HSA, by each of aparticular number of balls (e.g., similar to balls 202 c of FIGS. 4A-4C)of the bearing assembly riding in a corresponding respective start orthread of the same particular number of starts of the multi-start screw702 a, 902 a (e.g., similar to screw 202 a of FIGS. 4A-4C). Thus, asdescribed in reference to FIGS. 4A-4C, with the number of startsequaling the number of balls a stable planar “platform” is provided witha single bearing assembly perpendicular to the axis/translation path.

At block 1106, while the bearing assembly is translating, the verticalposition of the HSA is sensed. For example, as illustrated in FIGS.6A-6B a pair of proximity or position sensors 602 may be coupled to atleast one actuator arm 205, 705 and configured to sense the Z position(e.g., vertical height) of the actuator arm 205, 705 relative to amagnetic encoding strip and, ultimately, relative to the disk stack.

Extensions and Alternatives

In the foregoing description, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Therefore, various modifications andchanges may be made thereto without departing from the broader spiritand scope of the embodiments. Thus, the sole and exclusive indicator ofwhat is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

In addition, in this description certain process steps may be set forthin a particular order, and alphabetic and alphanumeric labels may beused to identify certain steps. Unless specifically stated in thedescription, embodiments are not necessarily limited to any particularorder of carrying out such steps. In particular, the labels are usedmerely for convenient identification of steps, and are not intended tospecify or require a particular order of carrying out such steps.

What is claimed is:
 1. An actuator elevator assembly for a reduced-headhard disk drive (HDD), the assembly comprising: a ball screw camassembly; a head-stack assembly (HSA) translatably coupled with the camassembly; and an axial flux permanent magnet (AFPM) motor affixed to ascrew of the cam assembly and configured to rotate about a fixed shaftaround which the AFPM motor is positioned, to drive rotation of thescrew to drive translation of the HSA along an axis of the screw.
 2. Theactuator elevator assembly of claim 1, wherein the screw of the camassembly comprises an upper flange to which an axial permanent magnetrotor of the AFPM motor is affixed.
 3. The actuator elevator assembly ofclaim 2, wherein the screw and the upper flange are composed of aferritic stainless steel material.
 4. The actuator elevator assembly ofclaim 2, further comprising: an integrated stator-top bracket assemblycomprising: a top actuator elevator assembly bracket comprising aplurality of AFPM motor stator core protrusions extending therefrom, anda plurality of AFPM motor stator coils each wound around a correspondingstator core protrusion of the plurality of stator core protrusions. 5.The actuator elevator assembly of claim 4, wherein the top actuatorelevator assembly bracket is composed of a soft magnetic composite (SMC)material.
 6. The actuator elevator assembly of claim 4, wherein the topactuator elevator assembly bracket is composed of a ferritic stainlesssteel material.
 7. A hard disk drive comprising the actuator elevatorassembly of claim
 4. 8. The actuator elevator assembly of claim 1,further comprising: an integrated stator-top bracket assemblycomprising: a top actuator elevator assembly bracket comprising aplurality of AFPM motor stator core protrusions extending therefrom, anda plurality of AFPM motor stator coils each wound around a correspondingstator core protrusion of the plurality of stator core protrusions. 9.The actuator elevator assembly of claim 8, further comprising: a lowerinner bearing assembly; an upper inner bearing assembly; and a bearinghousing coupled with and extending from the upper inner bearing assemblyto the lower inner bearing assembly; wherein an AFPM motor statorcomprising a plurality of AFPM motor stator coils each wound around acorresponding stator core protrusion is mounted to an outer diameter ofthe bearing housing.
 10. A hard disk drive comprising the actuatorelevator assembly of claim
 9. 11. The actuator elevator assembly ofclaim 9, wherein the screw of the cam assembly comprises an annular stepstructure extending radially inward from an inner diameter of the screwand to which an axial permanent magnet rotor of the AFPM motor isaffixed.
 12. The actuator elevator assembly of claim 11, wherein thescrew of the cam assembly is composed of a ferritic stainless steelmaterial.
 13. A hard disk drive comprising the actuator elevatorassembly of claim
 1. 14. The actuator elevator assembly of claim 1,wherein the ball screw cam assembly comprises: a hollow screw comprisingat least three starts, a ball bearing assembly comprising a same numberof balls as starts, wherein each ball rides in a corresponding start,thereby forming a plane on which the balls ride perpendicular to theaxis of the screw.
 15. The actuator elevator assembly of claim 1,further comprising: one or more proximity sensors coupled with the HSA;and a magnetic encoder strip positioned in close proximity to the one ormore proximity sensors, and configured to provide a magnetic field forsensing by the one or more proximity sensors.
 16. A method forvertically translating a head-stack assembly (HSA) in a hard disk drive(HDD) to access multiple magnetic-recording disks, the methodcomprising: driving an axial flux permanent magnet (AFPM) motor affixedto a screw of a ball screw cam assembly, thereby rotating the screwabout a coaxial fixed shaft; allowing a planar multi-ball bearingassembly that is coupled with the HSA to translate vertically inresponse to rotating the screw; and while the bearing assembly istranslating, sensing the vertical position of the HSA.
 17. The method ofclaim 16, wherein the AFPM motor is affixed to the screw by: an upperflange, of the screw, to which an axial permanent magnet rotor of theAFPM motor is affixed; and an integrated stator-top bracket assemblyover the rotor and comprising: a top actuator elevator assembly bracketcomprising a plurality of AFPM motor stator core protrusions extendingtherefrom, and a plurality of AFPM motor stator coils each wound arounda corresponding stator core protrusion of the plurality of stator coreprotrusions.
 18. The method of claim 16, wherein the AFPM motor isaffixed to the screw by: an annular step structure, extending radiallyinward from an inner diameter of the screw, to which an axial permanentmagnet rotor of the AFPM motor is affixed; and a bearing housing coupledwith and extending between a lower bearing assembly and an upper bearingassembly of the ball screw cam assembly, an outer diameter of thebearing housing to which an AFPM motor stator comprising a plurality ofAFPM motor stator coils each wound around a corresponding stator coreprotrusion is mounted.
 19. A reduced-head hard disk drive (HDD),comprising: recording means for storing digital information;reading/writing means for reading from and writing to the recordingmeans; means for moving the reading/writing means to access portions ofthe recording means; axial flux permanent magnet (AFPM) motor rotatingmeans for rotating cam means about a fixed shaft for translating thereading/writing means from one recording means to another recordingmeans; and means for sensing a vertical position of the reading/writingmeans.